WMOD00571

• Title: Static Mode Seeding of Convective Clouds - A Review
• Date: 5/23/1984
• Weather Modification - Doc Type: Report

With ground-based seeding the problems of seeding coverage, controlling
seeding concentrations, and targeting and timing of seeding effects become
even more difficult to overcome. Early studies (MacCready et al., 1957b)
report finding silver iodide particles from ground generators in sufficient
concentrations to produce seeding effects as far as 48 km from their source
in particular situations. McPartland and Super (1978) and Heimbach and
Stone (1984) found that silver iodide plumes from ground generators
ascended to cloud base altitudes in concentrations up to several orders of
magnitude above background during unstable conditions favorable for convec-
tion. However, Heimbach and Stone (1984) showed that targeting was dif-
ficult and the rising plumes did not disperse as much as expected from
theory. Admirat and Buscaglione (1982) measured ice nuclei concentrations
in updrafts just below cloud base of a storm being seeded with a dense net-
work of ground-based silver iodide-acetone generators and found values from
one-to-two orders of magnitude higher than those outside the experimental
zone. They also proposed the concept of a SSF (Storm Seeding Factor),
defined as the ratio of the artificial ice nuclei concentration below the
cloud base of seeded storms to the natural concentrations below unseeded
storms, to express the concentration of effective silver iodide nuclei from
ground-based seeding systems that enter the storm base after diffusion,
transport and deactivation. The SSF was computed for a large number of
ground-based seeding experiments yielding values from 1 to 500, with most
experiments being close to 1.

Another significant problem with ground-based seeding and, in fact, air-
borne patrol seeding at cloud base altitudes is that it is non-selective,

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